In the foundry art, cores and molds for use in making metal castings are commonly prepared from mixtures of an aggregate material, such as sand, which has been combined with a bonding amount of a polymerizable or curable binder. Frequently, minor amounts of other materials are also included in these mixtures, e.g., iron oxide, ground flax fibers, powdered coal, clay, and the like. The binder permits such a foundry mix to be molded to shape into the desired form and thereafter cured to form a self-supporting structure.
Typically, sand is used as the aggregate material. After the sand and binder have been mixed, the resulting foundry sand mix is rammed, blown, or otherwise introduced into a pattern, thereby assuming the shape defined by the adjacent surfaces of the pattern. Then by the use of a catalyst and/or the use of heat, the polymerizable binders polymerize or cure, thereby converting the formed, uncured, plastic, foundry aggregate mix into a hard, solid, cured state. This hardening can be accomplished in the original pattern or in a holding pattern.
Certain of the prior art processes are quite effective. Unfortunately, the use of core oil binders (e.g., "baking binders"), which are cured by being subjected to elevated temperatures, e.g., from about 225.degree. F. to about 500.degree. F., requires that heating facilities be available. Frequently, it is necessary to keep the green cores in the original molds or patterns during this heating period, since many heat-curable binders do not impart sufficient green strength to cause green cores to retain their desired shape without external support until such time as a final cure can be effected. Likewise, binders which are cured by means of gaseous catalysts often require that gasing chambers be available. Additionally, many of the binders which can be gas cured suffer from the same green strength or stripping strength deficiencies as do the heat curable binders.
In an effort to prepare cores without the necessity for using heat, gaseous catalyst, and the like, various prior attempts have been made to prepare binders which would be capable of curing at room temperature, i.e. at tempertures of from about 45.degree. to about 120.degree. F., more usually about 60.degree. to about 90.degree. F. A variety of materials have been developed or suggested for use as binders, but these prior compositions have suffered from one or more deficiencies.
Among the better performing systems are those employing furfuryl alcohol, which can be polymerized to a furan polymer. The primary undesirable aspect of using furfuryl alcohol systems is that such are relatively expensive when compared to other foundry binder systems. Accordingly, much effort has gone into finding additives which would render the compositions less expensive. However, many such additives result in a significant sacrifice in the performance level of one or more important characteristics or properties of the composition. Discovering materials which can be used as inexpensive additives without significantly degrading important properties of the composition is, therefore, a continuing effort.
For instance, various furfuryl alcohol-furan binder compositions have been modified with aromatic polyester polyols as disclosed in copending application Ser. No. 887,087, now U.S. Pat. No. 4,215,206 to Hanesworth et al, and assigned to Ashland Oil, Inc., the assignee of the present application. The specific compositions employed therein, however, are not reactive at room temperature, and when the polyester polyols employed therein are used in no bake furan systems, the work time and strip time is much longer than desirable.